Remote-control system



Nov. 13, 1951 G. w. BAUGHMAN REMOTE CONTROL SYSTEM 9 Shee ts-Sheet 1Filed April 30, 1949 ..J I 1 .L... Y m w 3 n u m w V m Z G n m m n n n ne n u u m n I u b kw m n G. x u m M .ww n n n M 7 F E -N n11 ES %wbfiwwwwsw fim w .KN. Q Q E a QR wx QR 3 SR HIS A TTORNIY Nov. 13, 1951e. w. B AUGHMAN REMOTE CONTROL SYSTEM 9 Sheets-Sheet 2 Filed April 30,1949 mi QR 7 u u n 7 u n n w u w n u w u v in fi fi fi v E1 7 RE g as waw n u n m n m u Q. Q n F m n n film .+Q. u u Q u fl w n V n .n n n F vn n n u c: u 4 n n M v m m m m n g n i Q g m m m m g u u n n u n u u nv, u m 2 n u m m n m m INVENTOR. George WBaugbma/n HIS ATTORNEY Nov. 13,1951 e. WUBAUGHMAN REMOTE CONTROL SYSTEM 9 Sheets-Sheet 3 Filed April50, 1949 INVEN TOR. flearg'e "(Ball g'llinan HIS A TTORNEY G. w.BAUGHMAN I REMOTEICONTROL SYSTEM Nov. 13, 1951 9 Sheets-Sheet 4 FiledApril '30, 1949 INVEN TOR. opge Baug'bmcm HIS A TTORNEY' Nov. 13, 1951G. w. BIAUGHMAN REMOTE CCNTROL SYSTEM 9 Shets-Sheet 5 Filed April 30,1949 ma i MQQ . INVENTOR. Gearge Wflaaybman BY I HIS ATTORNEY Nov. 13,1951 G. w. BAUGHMAN REMOTE CONTROL sY'sTEM 9 Sheets-Sheet 6 Filed April50, 1949 n v" n n n u u n n v NN 1 1 I J U m kwww MN MW R E W M u n u Hu u N a I. B Wu j k L g m m Q 3 n m, u 0 u. u m d w a 1 n u r r wm n m mm m QQ n n m m r m m w n. mm H E u u v v f .w QR g \m m RS QR h k U iKER 3% v ab ESQ -wawmuwmw IW- w 6Q 9 m1 fi k fimxk .R r v EE 4 ww ER 4%@R HIS ATTORNEY Nov. 13, 1951 Filed April 30, 1949 G. W. BAUGHMAN REMOTECONTROL SYSTEM 9 Sheets-Sheet 7 INVENTOR. George Wb'auglzman HISATTORNEY G. w. BAUGHMAN 2,574,774

REMOTE CONTRQL sysnamv 9 Sheets-Sheet 8 Nov. 13, 1951 Filed April 30,1949 INVENTOR. George WBaayb/man BY HIS ATTORNEY Nov. 13, 1951 G w.BAUGHMAN REMOTE CONTROL SYSTEM 9 Sheets-Sheet 9 Filed April 30, 1949INVENTOR.

n SQSM George "(Bally/21mm BY 111$ A 77 0mm Patented Nov. 13, 1951REMOTE-CONTROL SYSTEM George W. Baughman, Swissvale, Pa., assignor toWestinghouse Air Brake Company, a corporation of PennsylvaniaApplication April 30, 1949, Serial No. 90,627

4 Claims. 1 My invention relates to remote control systems, andparticularly to systems comprising a central station, a plurality offield stations, and means providing two-way communication between thecentral station and each field station.

Remote control systems of the type described must be arranged so that notwo stations can transmit at the same time. In accordance with myinvention, I prevent such transmission conflicts between field stationsby constructing each field station so that it can transmit onlyimmediately after it has been called by the central station. I preventtransmission conflicts between the field stations and the centralstation by two complementary arrangements. The first of these twocomplementary arrangements provides that when the central station and aparticular field station are both in condition to transmit messages toeach other, the message from the central station is given priority. Theother of the two complementary arrangements provides that when a fieldstation starts to transmit a message to the central station,transmission by the central station is discontinued until the message iscompleted.

The problem of preventing conflicting transmission by two stationssimultaneously in a remote control system of the type described isparticularly dilficult in those systems wherein a single communicationchannel connects all the stations. My improved system is applicable tosuch single channel systems generally, and furthermore is applicable toa single channel system wherein the single channel is a single radiofrequency channel. My invention is shown and described herein inconnection with such a single radio frequency channel system, althoughin its broader aspects it is not limited to use in a single channelsystem.

An object of my invention is to provide a remote control systemincluding a central station and a plurality of field stations eachhaving twoway-communication with the central station, and includingimproved means for preventing simultaneous transmission by two stations.

Another object of my invention is to provide an improved system of thetype described, in which the several stations are connected by a singlecommunication channel.

Another object of my invention is to provide an improved system of thetype described, in which communication between the several stations isaccomplished over radiowaves.

Another object of my invention is to provide a remote control system ofthe type described in which each station is provided with means forstoring a'message to be transmitted, and in which 2 the stations arecalled in sequence by the central station independently of the messagestoring means.

A further object is to provide a system in which the sequential callingof the field stations by the central station is interrupted only when amessage to be transmitted to or from a particular field stationis'stored at the time that station is called.

Another object of my invention is to provide, in each of the stations ofthe system of the type described, a master relay for determining Whetherthat station is to transmit or receive messages, and improved circuitsfor controlling the energization of the master relay.

A further object is to provide, in each station of a system of the typedescribed, a radio transmitter and a radio receiver, and improvedcircuits by which the master relay controls the receiver andtransmitter.

Another object is to provide, in each of the field stations in a systemof the type described, a delivery relay for determining whether themessages received by that station are to be delivered there, andimproved circuits for controlling said delivery relay.

The remote control systems disclosed herein illustrate my invention asapplied to a time code control circuit of the general type disclosed inLetters Patent of the United States No. 2,411,375 issued to Arthur P.Jackel on November 19, 1946, for Remote Control Systems, and otherissued patents. In this type of system as disclosed in the prior art,the central station and the field stations are connected by a line wire.Communication between stations takes place by means of timed currentimpulses sent over the line wire and spaced by time intervals. Eachcode, whether sent to or from the central office, comprises a stationselecting portion followed by a message portion. The station selectingportion determines the particular field station or the particular panelin the central office which is to receive the message. The messageportion determines the particular relays at the field station or at thecentral office panel which are to be actuated.

In the system described herein, I accomplish the foregoing and otherobjects of my invention by providing the central station and each fieldstation with a radio transmitter and a radio receiver. The radio codeimpulses may take the form of an unmodulated interrupted wave or theymay be a continuous wave modulated in any desired manner. A master relayat each station determines whether its transmitter or its receiver is tobe active and prevents both from being active simultaneously. The masterrelay at the central station is controlled to start transmissionwhenever the communication channel is inactive for a predetermined time.When the central station is actuated by the master relay to starttransmission, it first sends a station selecting code or call signals.The central station is provided with means for storing messages to besent to the respective. field stations. Each field station is providedwith means for storing a message to be sent to the central station. Eachstation selecting code or call signal transmitted by the centralstation. is. followed by an impulse whose length indicates whether amessage for that particular field. station is stored at the centralstation.

If a message is so stored, this impulse prepares the field station toreceive the message and, the transmission of the message follows, afterwhich the master relay at the central station. stops transmission.

If no message is stored at the central station, then the impulse whichfollows the field station call signal prepares the field station totransmit, providing a message is stored at the field station, and alsoterminatestransmission from the central station to prevent it frominterfering with the transmission by the field station. After themessage is transmitted by the field station, both stations stoptransmission.

If no message is stored at either the central station or the calledfield station, then all transmission stops after the impulse whichfollows the station call signal. The central station is provided withfield station selecting apparatus including a rotary selector switchwhich is advanced one step each time the central station goes through acycle of operation of its master relay. Thisapp aratus causes thestations to be called in a predetermined sequence which is endlesslyrepeated. The selection of the field stations by this apparatus isentirely independent of the storage of messages for particular fieldstations.

I shall describe one form of apparatus embodying my invention, and shallthen point out the novel features thereof in claims.

In the accompanying drawings, Figs. 1A, 1B, 1C, 1D and 1E, when arrangedas shown in Fig. 3, form a diagrammatic view illustrating one form ofcentral station equipment for a remote control system embodying myinvention. Figs. 2A,

2B, 2C and 2D when arranged as shown in Fig. 4, form a diagrammatic viewillustrating one form of field station equipment for the same remote.

control system.

The apparatus illustrated may be used, for example, as the centraloflice equipment in a railroad centralized trafiic control system, or itmay be used as a central station for controlling severalunattendedrepeater stations in a long diss tance communication system. Theparticular devices actuated at the field stations and the particularfunctions indicated at the central station form no part of my presentinvention, which resides in the remote control system for conveyinginformation between the central station and the field stations.

The system illustrated sends between stations codes consisting of one ortwo series of code steps. Each series of steps includes several timedimpulses spaced by timed intervals. Each impulse and each interval isreferred to hereinafter as onestep of the code. The odd steps areconsidered as impulses and the even steps as intervals between impulses.The system disclosed utilizes radio waves, andany form of unmodulated ormodulated waves may be used, provided only that the impulses bedistinguishable in some manner from the intervals. For present purposes,it will be assumed that the wave transmitted is continuous, and ismodulated during the impulses and unmodulated during the intervals.

The first series of steps in each code consists of eight code steps. Thefirst seven are utilized for calling a particular field station and theeighth is utilized for indicating whether or not a second series ofsteps forming a message for that stationis to follow. If so, the messageconsists of a second series of eight steps immediately following thefirst. If no message is to be sent to the station called, but a messageis to be sent by that station to the central station, it similarlyappears as a second series of steps immediately following the eighthstep of the first series, but is, of course, transmitted by thetransmitter of the field station. If no message is to be sent to orreceived from the station called, all transmission stops after theeighth step of the first series. When all transmission stops, the codeis completed, and after a brief period, the central station startstransmitting a new code which begins with the call signal of anotherfield station.

The codes are distinguished from each other for the purpose ofselectively calling the field station and for transmitting intelligenceby selectively varying the length of the code steps. The normal codestep is a short one and usually produces no controlling or indicatingfunction at the station receiving it. When a particular code step ismade long, it produces a particular control or indicating function atthe receiving station.

Central Station Equipment-Wigs 1A to 1E The central station equipmentincludes a coding unit, a pyramid unit, and a number of field stationpanels. The panel for field station I23 is shown at the right in Fig.IF... A portion of the pyramid unit is shown at the bottom of Fig. 1E.

. The rest of the apparatus appearing on Figs. 1A

to Hi: comprises the. central station coding unit.

In the drawings, the contacts of each relay are shown in verticalalignment with it. The reference character associated with each relayappears immediately above it. Where contacts are shown above a relaywinding, a dotted line extends upward through all the contacts and thereference character for the relay is again shown at the top of thecolumn of contacts. In showing the circuits, the letter B has been usedto indicate the positive terminal of a battery or other suitable sourceof electrical energy and the letter C has been used to indicate theopposite terminal.

The coding unit is provided with a counting;

The coding unit also includes a chain repeat relay CR, which isenergized on the eighth step of each code. If the code includes a secondseries of eightsteps, relay CR causes the counting chain relays. I to Ito be again picked up on the ninth to fifteenth steps, respectively, of

the code.

A series of impulse registry relays numbered 9 to 15, inclusive, arealso picked up on the ninth to fifteenth step of the code.

On the sixteenth step of the code, the counting relay 8 is. not.

picked up, butin its stead a code termination relay I6 is energized. I

There is provided a timing chain of slow release relays designated asIL, 2L, LP, LB, and LBP, which appear near the bottom of Fig. 1B. Theserelays all become energized during the first step of the code. As longas the station is sending or receiving short code steps, all theserelays remain picked up, although one or more of them may be deenergizedfrom time to time. When a long code step is sent or received, one ormore of these timing relays releases its contacts, depending upon thelength of the code step, and thereby completes a circuit for performinga control of indicating function, which function is selected inaccordance with the number of the long code step.

A master relay M (Fig. 1A) determines whether the central station is totransmit or receive codes. When master relay M is picked up, the centralstation is in condition to transmit. Front contact a of master relay Mthen connects an antenna I1 to the output circuit of a radio transmittergenerally indicated at I8. The input circuit of transmitter I8 iscontrolled by a front contact a of a transmitter relay T. At the sametime, front contacts 12' and c of master relay M place front contacts band c of transmitter relay T in control of the energizing circuit of areceiver relay R. (See Fig. 1B.)

When the master relay M releases its contacts, the central station is incondition tov receive. Back contact a of master relay M then connectsthe antenna lTto the input circuit of a radio receiving unit generallyindicated at I9, and the output circuit of the radio receiver I9 isconnected over back contacts b and c of master relay M to the energizingcircuit of receiver relay R. Also, when master relay M releases itscontacts, its front contact at opens the energizing circuit oftransmitter relay T.

Thus, when the central station is transmitting, the transmitter relay Tis intermittently energized over circuits to be described later, and thereceiver relay R follows the movements of the contacts of transmitterrelay T. When the central station is receiving, the transmitter relay Tis continuously deenergized, and the receiver relay R follows the codeimpulses received through the antenna I1 and the radio receiver I9.

Station selecting apparatus is provided at the central station includinga stepping switch gen-' erally indicated at 20 (Fig. 1E). The steppingswitch includes an insulating arm 2I fixed on a shaft 22 for rotationtherewith. The arm 2I carries three brushes 23. As the arm 2| rotates,the brushes 23 sequentially engage rows of contacts 24 supported by anannular insulating member, a portion of which is shown at 25.- One rowof contacts 24 is provided for each field station in the system; In thefragment of the station selecting apparatus shown in the 'drawings,contacts 24 areillustrated for field stations 55?, I23, and I24.

Each of the contacts 24 is connected to one of seven stations selectionterminals numbered 25-I to 25-1 (Fig. 1C). Only the connections for thecontacts 24 associated with station I23 are shown in the drawings. Itmay be observed that the outer one of those three contacts 24 isconnected by wire IIlI to terminal 25-I, the middle contact 24 by wireI02 to terminal 25-2, and the innermost contact by wire I03 to terminal25-3. The other connections have been omitted to avoid confusing thedrawings.

The shaft 22 also'carriesa ratchet wheel 26,

which is operated by a ratchet finger 21 at tached to an armature 28operated by an-electromagnet SM. The electromagnet SM is energized eachtime the master relay M picks up, and remains energized until thesending of a code is completed. When the electromagnet SM is energized,the finger 21 moves freely over the sloping side of one of the teeth ofthe ratchet wheel 26, and does not turn the shaft 22. When theelectromagnet SM is deenergized, the biasing spring 28a associated witharmature 28 moves the finger 21 downwardly, thereby rotating the shaft22 and arm 2I far enough to move the brushes 23 to the next set ofcontacts 24 corresponding to the next field station to be called.

The three brushes 23 are electrically connected together and to thebattery terminal B, as indicated in the drawings. The sequence switch 20is therefore effective in any given angular position to connect threeselected station selection terminals 25 to the battery terminal B. Inthe position of arm 2I shown in the drawings, the terminals 25-I, 25-2,and 25-3 are so connected. These connections cause the first, second,and third steps of the code to be made long, in a manner to be describedmore completely hereinafter. When the first, second, and third stepsareso selected, the apparatus at field station I23 responds in a mannerto be described later. Thus it may be seen that the station selectionapparatus including the sequence switch 20 causes the central station-tocall first one field station and then another, in a sequence determinedby the connections between the station selection terminals 25 and thecontacts 24, and that this sequence is endlessly repeated.

During the station selecting portion of a code, the central station isalways transmitting, and so the transmitter T controls the receiverrelay R. The relay R then controls the energization of station selectionchecking relays, commonly called pyramid relays, a group of which isshown in the pyramid unit at the bottom of Fig. 1E, and identified asrelays E, IF, and I 2G.

Relay E is termed the pyramid entry relay. There is only one relay E.The E relay is energized on the first step of every code, regardless ofwhether that step is short or long. A number of .F relays are provided,corresponding to the num ber of initial digits which appearv in thestation selecting codes. For example, in a system of the type shown,three code steps are used for each station code call and there are sevenstation selecting code steps available. Consequently, station code callsmay begin with any digit from 1 to 5. Consequently, there may be, insuch a system, as many as five F relays, numbered IF, 2F, 3F, 4F, and5F. Only relay IF is shown in the drawings.

In a complete system, a number of G relays are provided corresponding tothe number of combinations of two digits with which the code calls maybegin. In the present system, up to fifteen digit combinations may beused, and a corresponding number of G relays may be required. Only relayI2G is shown in the drawings.

A station relay I238 is provided for each central station panelcorresponding to a field station. In the system shown, up to thirty-fivefield stations may be used with one central station. The central stationhas one panel for each field station, similar to the panel for station I23 shown in Fig. 1E. Each field station panel at the central station hasits own S relay such as I238.

7? Each of the several station ,relaysi such as I 2 BS is: provided.with al front contact a ;.which controlswan. energizingcircuit ion-a.station repeater relay SP located inzthescentral station coding unit. Aportion, ofthiscircuit may be-traced from contact a of relay l 2 35.:over a; terminal, 29 Ofapanel for station l23 -and. a.terminal. 30 of.thegcentral station coding unit tothe windingof relay; SP. ItShOllldfbB. understood that terminal J 30- -.is=;similar1y connected:to; terminalsv'equivalent: to terminals 29 01112111513118 otherfieldstation. pane elsin-thementral station;

Each field i stationpanel at, the,:central. station is provided with 1one or more control-levers, such 1 as-:-those showndiagrammatically at3| and: 32 inFis. 1B: These. controllevers are provided:for thespurpose-toicontrolling; corresponding: functionsi-atthe field-stations;After a'control lever,

such as. 3I, hasbeen set to a position correspondingto a'.functiondesired to be'performed atthefield-station, then, a;starting. button.33onthe. central, station panel must be depressed momentarily-in-order-.-to cause the transmission-era con=- trol code tothe-field station correspondingto-the.

newpositionof the controljlever 31. The starti button 33 controls anobvious energizing circuit" Wherever" a terminal on the central stationcoding unit, such as terminal 35, for example, is illustrated'as beingconnected to a terminal, such as 34, onthe panel forstation 123, itshould'be understood that a similar connection exists betweenrthatcoding unit terminal'and'counterpart terminals on all the other panels.Similar con-- nections" are intended in the case of groups of terminals;such as the control terminals 36 on' the;.coding unit and the controlterminals 31 on the panel, where the actual connections betweenterminals 36 and 31are not shown on the drawings; but are indicatedbythe use of correspond inglegends.

Each of the control terminals 31 onthefield station panel is connectedto one of the control levers. In the case of the-panel for field stationI23, only two such connections are shown, since the-panel has onlythe'two control levers 3| and 32.

Thea-central ofiice coding unitis also provided with a set ofindicationterminals 38' 'connected to indication terminals 39'on the various fieldstation panels at the central station. The respective indicationterminals 39 are connected to indication stick relays, such as thoseillustrated at IK and4K. These relays-control energizingcircuits forindicator lamps and '42, respectively.

The energizing circuits for the ST and'S'relays include a similararrangement of station check terminals 43 on the central station codingunit which are connected to station checkterminals 44 on the centralstation pyramid unit. Since there is only one pyramid unit atthecentralstation ;.only one terminal 441s: connected to. each of.

the terminals 43.

Thepanel fOI'rEflQh field station includes alresetbutton 49swhichhasanormally closed'contact' in": the stick circuit for relay I23ST. Thereset button 49vmay be used-to oountermand the-push -v ingpfthei-starting'button 33,- in case-itis;desired.

topreyentthe. sending ot; a code to station. I23.

Field station equipment Most; of; the elements; of field. stationequip-- ment :shown in. Figs; 2A to 2D are the.counter.--

partsoff corresponding elements. at the central station: These field-jstation elements: have been given thesame .referencezcharacters astheir. cen;-

tral station. counterparts; preceded by the refer,- ence letter F. Inthe case of the station selec tion: relay IS, the. numerical prefix ofits central station .counterpart has 'beenidropped instead of addingitheprefix letter F.

The-field station starting relay'FST is con-- trolledrin amanner'somewhat difierent from the central station starting relays suchas I23ST. The Winding of relay FST is shunted by a choke coil 45iso-astomake the relay FST quick releasing. Relay FSTis provided with a pickupcircuit'wh'ich energizes it whenever a code is trans-- mitted' bythe'field station, and a stick circuit which maintains it energized untilacontact a of a function repeating relay such as IR, changes itsposition. A number of such function repeating-relays may be provided atthe field station. When any one of those relays changes its position,the starting relay FST is deenergized and causes the field station torespond to the nextreceipt of its station call signal by transmittingacode which indicates theposition. of all the function repeating relays.This code is effective.v the central station to position the indication.

relays such as IK tocorrespondto the position of their respectivefunction'repeating. relays at the field'station.

The field delivery relayFD is picked up after the.:eighth step of acode, providing the eighth step is of a length .indicatingthat a controlcode for the field'station is to. follow. Whenrelay FD picksup, itplaces a pairof impulse registry relays lAand 2A under. the.control of.the follow.- ing codestepsso thatrelay lAispickedup when-.- ever along.odd-numbered code step. is received and relayjA is pickedupwhenever. a long even-.-

numbered code step isreceived. The. impulse. registry relays I A and2A,. together with. the.

counting chain relays, |.-to..1,- control. energize ing circuits foranumber of. functionv control.

relays, two of which are shown .at I SR and 48B. Thefunction controlrelays are. energized or. de-

energized dependingupon whether their. respec- I tive steps of the codeare madelong or short.

Operation Having generally described the central station.

equipment and the field'station equipment, Iwill now describe threediiferent typical operations which.occur duringthe functioningofv thissys-. temp.

The firstoperation to. be described comprises.

the sending ofa station selecting-code only by the, central. stationand.the receipt of that code.

by the. field station.v In thisloperation the .station selectingcodewill' not be followedby a control code transmitted from the centralstation to the field. station nor. willit be followed by an.

indication .code transmitted .from the field sta-. tion to the centralstation.

The second operation to be described will comprise the sending of astation selection code by the ofiice, followed by a control code, andthe receipt of that station selecting code and control code by the fieldstation.

The third operation to be described comprises the sending of a fieldstation selecting code by the office followed by the transmission of anindication code from the field station to the central station.

These three operations will completely illustrate the functioning of mycontrol system. While particular codes may produce the selection ofdiiferent field stations or the performance of different control orindicating functions, nevertheless the operations to be described aretypical of all operations of the system.

In the description that follows, it is considered that each code stepbegins with the picking up or dropping of the receiver relays R and FRat the central station and the field station, respectively, and thatthese code steps end when these relays change their position in theopposite sense.

Ofi'ice sending call signal only for station 123 This call signalcomprises a code of eight steps, the first, second, and third stepsbeing long and the next four short. The eighth step is long, indicatingthat no control code is following from the oflice. Since no indicationcode is to follow from the field station, all transmission ceases afterthe eighth step.

Starting with thestepping switch and all the relays in the positionsshown in the drawings, it may be seen that a pickup circuit is completedfor master relay M. This circuit may be traced from battery terminal Bin Fig. 1A over back contacts a of relays IL and 2L, thence through thewinding of relay M and through wire 46, terminals 41 and 48, and thecontact of the reset button 49 on the field station panel to theopposite battery terminal C. Energization of relay M causes it to closeits front contacts. Front contact a of relay M connects antenna H to theoutput circuit of the radio transmitter I 8. Front contacts I) and c ofrelay M place the receiver relay R under the control of contacts I; andc of the transmitter relay T. The central station is thus prepared totransmit a code. Contact e of relay M completes an obvious circuit overwire 91 for electromagnet SM of stepping switch 20.

As previously mentioned, energization of electromagnet SM produces noaction, but prepares the stepping switch 20 to move along to its nextstation selecting position when the electromagnet SM is deenergized.Contact I of relay M prepares a stick circuit for that relay which maybe traced from battery terminal B (Fig. over back contact a of relay I6,back contact a of relay 8 in parallel with front contact a of relay STP,and thence over a conductor 49, front contact a of relay LB in parallelwith front contact 1 of relay LBP, front contact J of relay M, throughthe winding of relay M and thence along the circuit previously traced,to battery terminal C. Relay M is made slow releasing by the connectionof an asymmetric unit across the terminals of its winding, so that itcan hold its contacts in their picked-up positions during the timebetween the picking up of relay EL which breaks the pickup circuit ofrelay M and the picking up of relay LB which completes its stickcircuit, as described below.

Front contact 01 of relay M closes a pickup circuit for transmitterrelay T which may be traced from battery terminal B (Fig. 10) over backcontact a of relay [6, back contact a of relay 8 in parallel with frontcontact a of relay STP, thence over back contacts ,1 of relays 1, 5, 3,and. I, wire 50, front contact 01 of relay M, and thence through thewinding of transmitter relay T and fixed resistances 5| and 52 to theopposite battery terminal C.

When relay T picks up, its front contact a completes the input circuitof radio transmitter I8, thereby initiating the transmission of animpulse to the field stations. At the same time, contacts I) and c oftransmitter relay T complete an obvious energizing circuit for receiverrelay R, which picks up, thereby starting the reception at the office ofthe first step of the code.

Contact d of relay T prepares a number of parallel stick circuits forrelay T, which may be effective to maintain energization of relay Tduring the long odd-numbered code steps. Two of these circuits may betraced from battery terminal B at stepping switch 20 (Fig. 1E), thencethrough brushes 23 and contacts 24, wires Ifll and I 03, terminals 25Iand 25-3, front contacts a of relays I and 3, back contact a of relayCR, and thence through wire 5|, front contact d of relay IL in parallelwith front, contact a of relay LP, over front contact d of relay T andthence through the winding of relay T and resistances 5I and 52 to theopposite battery terminal.

Front contact e of relay T shunts resistance 5| from the stick circuitof that relay. When back contact e of relay T is closed, it prepares anumber of parallel hold-down circuits for relay T which may beselectively closed during the long even-numbered cod steps. One of thesehold-down circuits may be traced from terminal B at sequence switch 20through the center brush 23, contact 24, wire I 02, terminal 25-2, frontcontact a of relay 2, back contact b of relay CR, conductor 52, frontcontact 1 of relay 2L in parallel with front contact 0 of relay LP. overback contact e of relay T and through resistances 5| and 52 to theopposite battery terminal C. When any of these hold-down circuits iscompleted, the winding of relay T is effectively shunted, and cannot bepicked up by completion Of its pickup circuit.

First code step.--When relay R picks up to initiate the first code step,its front contact a completes a pickup circuit for slow release relay ILin the timing relay chain. -This circuit may be traced from batteryterminal B (Fig. 13 over front contact a of relay R, back contact b ofrelay 2L, back contact a of relay LBP, and the winding of relay IL tothe opposite battery terminal C. When relay IL picks up, its backcontact it opens the pickup circuit for master relay M whichnevertheless remains up due to its slow releasing characteristics untilits stick circuit, previously traced, is completed. When relay IL picksup, its contact b completes a pickup circuit for counting chain relay I,and its contact 0 completes a pickup circuit for the slow release relay2L.

The pickup circuit for relay I may be traced from battery terminal Bover front contact b of relay R, back contact I) of relay LBP, frontcontact b of relay IL, wire 53, and through the winding of relay I tothe opposite battery terminal C. Picking up of relay l completes apickup circuit for pyramid entry relay E, which may be traced frombattery terminal B (Fig. 1B) over back contact 0 of relay LBP, wire 54,contact I) of -:-re1ay 3|, wires98, and the winding. ofnrelayeE to':-battery terminal C. The;picking ,up--=,of:.relay. I

.;-also completes over. its"frontcontact a-,--and-front contact 01' ofrelay IL the previouslyztraced stick i-ioircuit for transmitter relay T.Relay now re- -.-.mains-energized until this stick circuit'is broken.

-I-Ience, .thisstick circuit determines the length of the first codestep.

:When relay. 2L picks up due :tothe closing of tits gpreviouslytracedpickup circuit over .front .contact I) .ofrelay 4L; back contact.I) of relay "2L opens. thepickupmircuit for relay iL. Relay ILvcon-tinues'to-hold =its contacts up fora time be- -.eause.of its slowreleasing characteristics. When .relay:ZLpicks.up,-..it.completes-itsown'stick cir- .cuit at-its-front-contact c. lt'also' completes. a.oircuitfor relay.LP over-front contacteof relay .JLand front. contact-dof relay-2L. When relay ..LP .picks:up,; itcloseswits front contactc inparwallel-withfrontcontact d of relay ILin" thestick circuit for.transmitter relayT. .This insures that the energization. of relay .T andhence .the first :code. step will continue 1 until both relays -iL andllRaredeenergized. .Front:contact b of relay LP closes .anobvious..pickup.- circuit for -:relay .LB

and another obviouspickup circuit forrelay.LBP

-whichextends .over backcontact a of. relay. LB. When relay LB .picks.up, thisoriginal energizing circuitfor relay LBP. is replacedbyone overfront contact a...of relay.LB.

Picking up of relay LBP opens the previously traced .pickup..circuit.for relay E .at back con- .tact'c of.,relay,LBP. Howeventhesame action.also. completes ,a -stick circuit for. relay E -which .may betracedlfrombatteryterminal B .(Eig..1B)

.over. front contact c of. relay LBP,v wire .55,..back .contact a ofrelay. SP, terminalfifi, terminalb, .back contact-a of. relay..IE',.frontcontact aof re- TlayjE, and through the-winding of..relay-E totheoppositeQbattery .terminal C.

breaks the previously traced pickup-circuit vfor counting "chain relayI, but itsirontcontactb establishesa stickcircuit'for. relay. I. Thisstick circuit may be traced from battery terminal B (Fig..1'B) overfront contact b of relay R, front contact b of. relay LBP, wire60,jbackcontact/l of. relay 2, front contact e of relay I and through theWinding of relay I to battery terminal (3.

. Relay IL now drops as a result of its previous cle- 'energization Whenre1ay'2L picked up, and its back contactf completes apickup. circuitfforrelay" IF. This circuitLmay be tracedfrorni battery terminalBiFig. 1B).over front contact 0 of relay LBP, back contact '1 'of relay i.IL,'conductor' 59, back contact 0 of relay CR, front contact, 0 of-countin'g'chain relay I,terminals'43- I (Fig; 1D) and id-+1 (Fig-1E)front contacthof relayE, and thence through the winding 'of' relay IF tothe opposite batteryterminal C. Relay IF'picks up -and'closes itsown-stick-circuit at itsfront contact I). This stick circuit may betraced from battery terminal 'B (Fig. 113) over front" contact 0 ofrelayLBP,- wire 55, back contact a of relay SP, terminal 56, terminal 58,back contact a of 'relay I'2G;front'contact b of'relay iF-and throughthe winding of relay IF to battery terminal C. 'Relay IF in picking upalso opens its back contact a, therebybreaking the stick circuit'forrelay E, which drops, and breaks the pickup circuit just traced forrelay I F.

When relay IL dropped, it opened the energizing circuit'for relay LPwhich, however, held its contacts up because ofits slow releasingcharacteristics, which are designed to be long enough to maintain thecontacts of relay LP up until after 40 When relay LBP, picks .up,its'back contact .b

thestick circuit'for relay IF, just traced,1.has been established..Thereafter,.relay; LP' releases its contacts, and its front.contact abreaks-the previously traced stick circuit for transmitter; relay T.Transmitter relay T thereupon releases its contacts,'opening'the radiotransmitter 'input'circuit'at' its front contact a and opening theenergizing circuit of relay R at its front contacts b and 0. Relay Rdrops, terminating the impulse which constitutes the first step of the.code, and starting the interval which:constitutes the second step ofthe code.

Second code step.--When relay-Rdrops to, start the second code step,.its front contact a-breaks the stick circuit for-relayZL, and its frontcontact 7) opens the stick circuitfor. counting relayd. At the sametime, back contact 0 of relayR. closes apickup circuit. for relay.IL,.andback contact at of relayR c1oses..a pickup .circuitforcountingrelayfi. Relay.2L.continues to hold its contacts up because .of theslow. releasing .characteristics imparted by. the asymmetricunitconnected across the terminals ofitswinding. Relay I continues to holdits contacts up until its stick circuit is opened at back contact clofrelay'zydueto'the slow releasing characteristics impartedbyasymmetricunit .SI connected .between wire 60 and battery terminal C.

Thecircuit over which relay .IL.is.picked up on the second code. stepmay. betraced from battery terminal B .(Fig. 113) over. back contact cofrelay R, front contact 6 of .relayZL inparallel with front contacta ofrelay LBP; andthence through thewinding of relay IL to battery ter-:minal C. Picking upof relayjILagain completes .the pickup circuit forrelay LP over front contact e of relay EL and front. contact d of relay2L.

The pickup circuitfor relay 2 maybe traced over back contact dof relay.R, front contactjd of. relay LBP, wire 62, back contactepf countingrelay 8, fronticontact d.of relay 'I,..and thence .through the windingof relay $2 to battery.ter-

minal C. 'Relay 2 completes its stick circuitover its contact e and backcontact 01 of relay 3. "Relay .2 in picking up closes at itsfront.contact. a one or the hold-down circuits for transmitter relay T,-previously traced. .It will be remembered that this circuit extendsfrom .positive battery terminal iB'at stepping switch 20 over wire I02;terminal '252, contact a of relay2, back contact'bof relay CR, wire 52,front contact f'of relay 2L inparallel with front contact 0 of relay.LP,and over back contact "e of relay T to the negative terminal of itswinding. This circuit applies the positive battery terminal -to thenormally negative terminal of'thewinding of relayl'I, and prevents thatrelay from picking up even whenits pickup circuit'is completed. Thisstick-down circuit insures that relay Tremainsdown until relays 2L. andLP both drop their contacts to open the hold-down circuit.

"Relay 2 injpicking up opens at its back contact 'dthe connection bywhich asymmetric unit-6| was connected across the terminalsof' thewinding'of relay I, so that'relay I immediately drops. The droppingof-relay I completes at its back contact f the pickup circuit fortransmitter relay T, but this circuit is at present ineffective becauseof the hold-down circuit for that relay, just traced.

Relay 2L, having been deenergized whenrelay R dropped, now'releases itscontacts, thereby opening the circuit for relay LP-and closing a pickup'circuit for relay IZG. Relay LP continues'to hold its contacts upbecause of its slow releasing 'characteristics. -'I'hepickup'circuit'forrelay IZG may be traced from battery terminal B (FigJlBy over frontcontact 0 of relay LBP, back contact 9 of relay 2L, wire 63, backcontact d of relay CR, front contact 0 of relay 2, terminal 43-2 (Fig.1D) terminal 44-2 (Fig. 1E) front contact 0 of relay IF, and thencethrough the winding of relay I2G to battery terminal C. Relay I2G inpicking up opens the previously traced stick circuit for relay IF at itsback contact a, and closes its own stick circuit at its front contact a.This stick circuit for relay I2G follows the previously traced stickcircuit for relay IF to front contact a of relay I 2G, and thence passesthrough the winding of relay I2G to battery terminal C.

Relay LP, having been deenergized when relay 2L dropped, now releasesits contacts, thereby opening at its contact 0 the hold-down circuitpreviously traced for transmitter relay T. The pickup circuit for relayT through back contact J of counting relay I then becomes eifective toenergize relay T, which picks up, thereby energizing relay R whichlikewise picks up. The code interval which constituted the second stepis thereby terminated and the code impulse which constitutes the thirdcode step is started.

Third code step.--When relay R picks up, its back contact 0 opens thecircuit for relay IL and its back contact d opens the stick circuit forrelay 2. Relay IL continues to hold its contacts up because of its slowreleasing characteristics. Relay 2 also continues to hold its contactsup because of the slow releasing characteristics imparted to it by therectifier 64 which is connected across the terminals of relay 2 throughits front contact e and back contact at of relay 3. When relay R picksup, its front contact a completes the pickup circuit for relay 2L, whichalso extends over front contact 0 of relay IL. At the same time, frontcontact I) of relay R completes a pickup circuit for relay 3, which maybe traced over front contact b of relay R, front contact b of relay LBP,wire 60, back contact e of relay I, front contact (1 of relay 2, andthence through the winding of relay 3 to battery terminal C. Relay 3completes its stick circuit over its contact e and back contact d ofrelay 4.

When relay 2L picks up, it completes the circuit for relay LP,previously traced. Relay LP thereupon picks up its contacts.

When relay 3 picks up, its back contact at opens the connection by whichasymmetric unit 6I was connected across the terminals of the winding ofrelay 2, so that relay 2 then quickly releases its contacts.

Relay 3 in picking up opens the pickup circuit for relay T at backcontact J of relay 3. However, front contact a of relay 3 completes astick circuit for relay T, previously traced, over front contact at ofrelay IL and front contact a of relay LP in parallel, almost immediatelyafter the pickup circuit for relay T is broken. Relay T is madesufficiently slow releasing so as to bridge the gap between the timewhen its pickup circuit is opened and its stick circuit is closed, andtherefore holds its contacts up during this interval. Relay T is nowstuck up, and cannot release its contacts until both relays IL and LPrelease their contacts.

Relay IL, having been deenergized when relay R picked up, now releasesits contacts, thereby opening the circuit of relay LP, which continuesto hold its contacts up because of its slow releasing characteristics.When relay IL releases its contacts, its back contact completes anenergizing circuit for relay I238. This circuit may be traced frombattery terminal B (Fig. 1B) over front contact 0 of relay LBP, backcontact f i 14 of relay IL, conductor 59, back contact 0 of relay CR,front contact 0 of relay 3, terminal 43-3, terminal 44-3, front contactI) of relay I2G, and thence through the winding of relay I23S to batteryterminal C.

Relay I23S in picking up closes at its front contact a an energizingcircuit for relay SP. This circuit may be followed along the circuitjust traced for relay I23S and thence over front contact a of thatrelay, terminals 29 and 30, through the winding of relay SP to batteryterminal C. When relay SP picks up, its front contact a opens the stickcircuit previously traced for relay I2G and completes stick circuits forrelays SP and I23S. These stick circuits may be traced from batteryterminal B (Fig. 13) over front contact 0 of relay LBP, through wire 55,front contact a of relay SP, and thence either through Winding of relaySP to battery terminal C or through terminals 30 and 29, over frontcontact a of relay I23S, and thence through the winding of that relay tobattery terminal C.

Relay LP, having been deenergized when relay IL released its contacts,now releases its contacts in turn, and its front contact a opens thestick circuit for transmitter relay T, which consequently drops. Thisdeenergizes relay R which releases its contacts to terminate the impulsewhich constitutes the third step of the code and to start the intervalwhich constitutes the fourth step.

Fourth. code step.--When relay R drops, its front contact 0. opens thecircuit for relay-2L, and its front contact b opens the circuit forrelay 3. Both relays 2L and 3 continue to hold their contacts up becauseof their slow releasing characteristics. When relay R drops, its backcontact c completes a circuit for relay IL, and its back contact (1completes a pickup circuit for relay 4 which may be traced over backcontact e of relay 2 and front contact d of relay 3. Relay completes itsstick circuit in a similar manner to the counting chain relays 2 and 3.The stick circuits for relays 4, 5, 6, and I will not be described indetail, as they are all believed to be obvious from the drawing.

When relay IL picks up, it completes the cir cuit for relay LP, whichalso picks up.

When relay 4 picks up, its back contact at opens the connection by whichasymmetric unit BI shunts the winding of relay 3, and relay 3immediately drops. When relay 3 drops, its back contact completes theenergizing circuit for transmitter relay T. Since no hold-down cir cuitthrough sequence switch 29 and contact a of relay 4 is completed, thisenergizing circuit for transmitter relay T is immediately effective andit picks up relay T. Relay T in turn picks up relay R to terminate theinterval which constituted the fourth step of the code and to start theimpulse which constitutes the fifth step.

It should be noted that the fourth step was much shorter than theprevious steps and was not dependent upon the release times of therelays IL, 2L, and LP. The release time of relay 2L is such that it hasnot released its contacts at the end of the fourth step, andconsequently relay LP remains energized.

Fifth code step.-When relay R picks up, its back contact 0 opens thecircuit for relay IL and its front contact a completes the circuit forrelay 2L. Since relay 2L had not released its contacts at the end of thefourth step, it may be seen that the contacts of relay 2L, and likewiseEL, remain up continuously as long as. the code =35 steps remain short.Consequently, relay -re- .mains energized as long-as the code steps areshort.

When relay R picks up at the beginning the fifth step, its back contactd-opens the circult-for relay 4 and its front contact b completes =acircuit forrelay 5. When relay 5 picks up, its back contact I) opens andimmediatelydrops relay 3. At-the same time, back contact f of relay 5opens the pickup circuit of transmitterrelay T. Since no stick circuitfor relay T is completed at this time through the sequence switch 20,r'elayT-drops after a period-of time determined by its slowreleasingcharacteristics, thereby deenergizing relay-R to terminate thefifth code step and start the sixth.

Sixth code step.-#This step is like the fourth code step, except thatthe countin relay 5 is dropped and the counting relay 6 is picked up, ascompared with the dropping of relay 3 and picking up of relay 4 on thefourth step.

Seventh code step-"This step is like the fifth step, except thatcounting relay-6 is dropped and counting relay is picked up, as comparedwith the dropping of relayl and picking up of relay 5 on'the fifth step.

Eighth code step.When relay R drops at the 'beginningof thisstep,itsback contact c recloses the circuit for relay lL, therebyreenergizing it to hold its contacts up. Front contact a of relay Ropens the circuit to rela 2L, which continues to holdits contacts upbecause of its'slow releasing characteristics.

Opening of contact b of relay R opens the circuitto'relay'l. Closureofiback contact (Z of relay R completesa pickup circuit for relaysimilar to the pickup circuits for relays 2, (i, and li except that itincludes back contact e of chain repeat relay CR. When relay 8 picks-up,its "backcontact d opens the connection by which asymmetricunit 5| isconnected across thewinding of'relay-"l, so that relay 1 then drops itscontacts.

When relay 8 picks up, its front contact b completes a pickup circuitfor the. chain repeat relay CR which may be traced from battery terminali l? (Fig. 1B) over front contact'c of relay LBP, wire 55, frontcontactb'of relay SP (-Fig. 1E), wire '51, frontcontact b of relay 8,-and thewindingof rela CR to the battery terminal C.

When relay 8 "picks up, its front contact :1 opens both the stickcircuit of maste relay M and'the;pickup circuit of transmitter relay T.Therefore transmitter relay'T cannot pick up to continue transmissionbeyond the eighth step. The 'masterrelay M continues to hold itscontacts up for a time'determined by its slow releasing characteristicsbefore it drops to transfer controlof receiver relay R to the radioreceiver 19.

At the beginning'of this'operation, it was assumed that no message wasstored at the central station'byenergization of relays I23ST and STP andthat no message was stored at the field station 123 which would cause itto transmit at this time.

. Relay 2L, havin been deenergized by the dropping of relayR'at thebeginning of the eighth step, now releases itscontacts. RelaysLP, andLBP then releasetheir contacts in order, each after a time determined byits own slow releasing characteristics.

When the LBP relay drops, its front contact 0! opens the circuit torelayS, and its front contact i-c'opens the circuit to relays l23S, SP,and CR. fContact a'of relay...LBP opens the circuit i ii to relay l L,but itscontacts'remainup for a-time because of its slow releasingcharacteristics.

When relay M releases its contacts, it front contact e opens-the circuitfor-electromagnetSM and the stepping switch 2 El, thereby 'deenergizingelectromagnet SM and causing the pawl "21 to advance the ratchetwheel'fi, thereby moving the arm 2| so that field station 2 will beselected when the central station transmits its next code.

When relay lL'drops, thenall relayshave been returned to their positionsat the beginning of the codes just described, and asjuSt' mentioned-thestepping switch 2!) has been'advanced one step. When relay lL 'drops,its contact a completes the pickup circuit for master relay M which:picks up to start transmission of the call signal for the station I'M,as selected by thestepping-switch-Zfl.

Field station'123 receiving itscall signal only We will now consider theoperation of .the'jfield station equipment. shown in Figs. 2A to ZDwhenreceiving the station call signal whose transmission by the centralstation has just been 'described. It isassumed that the operationstartswith .all the relays inthe positions shownin the drawings. Hence theradio receiver TFiElfhas its input circuit connected to the-antennaFl'lover back. contact f of relay FM, and its outputcircuit is connectedto the fieldreceiver relay'FRover back contacts d and e of relay FM.

First code step-Fieldreceiver relayFRpicks up as the first transmittedimpirlsefromthe central station begins, and remainsup throughout theimpulse. When relay FR .picksup, ,its'front contact a completes apickupcircuitfor. counting chain relay FIL. This circuit may be tracedoverfront contact a of relay FRyback contact a o'f relay FZL, and backcontact aiofrelayFLBP. When relay FlL picks up, .its'front contact acloses a pickup circuit for relayFl ofthecounting chain. This circuitmay be tracedover front contact I) of relay FR, back contact 1) of relayFLBP, front contact a of relayFlL, a resistance 65, a Wire 66, andthrough the winding of .relay Fl to the opposite battery terminal C.

Front contact I) of rela -FlL closes an' obvious energizing circuit forrelay'FZL, which in turn closes its stick circuit over its own frontcontact b. Opening of back contact a of relay FZL .1 breaks the circuitof relay FlL, which holds its contacts up due to its'slow releasingcharacteristics.

Picking up of relay F2L completes a circuit-for relay'FLP over frontcontacts 0 of relays'FlL and FZL. Picking up of front'contact a of relayFLP completes a circuit for relay FLB and another circuit for relayFLBPwhich extends over back contact a of relay FLB. This last circuitjisimmediately replaced by another circuit over front contact a of relayFLB when the latter picks up.

When relay FLBP pick up, the pickup circuit previously traced forcounting chain relay Fl is broken by the back contact I) of relay 'FLBP.However, this pickup circuit is immediately replaced by a stick circuitfor the same relaywhich may be traced over front contact b of relay FR,front contact 12 of relay FLBP, a resistancefi'l. wire 58, back contacta of counting chain relay F2, and front contact b of countingchain'relay Fl.

This first code step is longer than the release time of relay'FlL,which, having been deenergized by thepicking up of relay FZL, releasesits contacts when its release time expires. It back l9 Seventh codestep:-.'This is generally similar to the fifth code step, except thatrelay F6 is dropped and relay FI picked up, ascompared to the droppingof relay F4 and picking up of relay F5 on the fifth code step.

Eighth code step.When relay FR drops, its front contact a opens thecircuit for relay F2L and its front contact 1) opens the circuit forrelay F'I. At the same time, its back contact 0 completes a circuit forrelay FIL and its back contact d completes a circuit for counting chainrelay F8. The pickup circuit for relay F8 may be traced from backcontact d of relay FR over front contact d of relay FLBP, resistance 14,Wire 15, back contact b of relay F6, front contact a of relay F1, backcontact b of relay FCR, to the winding of relay F8.

When relay F8 picks up, its front contact b completes a pickup circuitfor relay FCR. This circuit may be traced over front contact 0 of relayFLBP, wire 69, front contact a of relay S, and front contact 0 of relayF8 to the winding of relay FCR. Front contact d of relay FCR completesits stick circuit over front contact 0 of relay FLBP.

The interval between impulses which constitutes the eighth code step iscontinued long enough by the central station to drop all the relays ofits counting chain in sequence. Consequently, the counting chain relaysat the field station also drop their contacts in sequence. Relay F2L,having been deenergized when relay FR dropped its contacts at thebeginning of the eighth step, is the first to release, followed insuccession by relays FLP, FLB, FLBP, and FIL. When relay FLBP drops, itsfront contact 0 breaks the stick circuit for relays S and FCR, and itsfront contact d breaks the circuit for relay F8. When these relays drop,all the relays and circuits at the field stations are returned to theirnormal positions, as shown in Figs. 2A and 23.

Operation with central station sending station call signal 123 followedby a control code In the following stage of operation of the system, itis assumed that the control levers 3I and 32 on the control panel forfield station I23 (see Fig. 10) have been moved to their circuit closingpositions and that the starting button 33 has been pushed momentarily topick up relay I23ST. Relay I23ST remains stuck up over its own frontcontact I) and back contact 0 of relay I238. The relays and the circuitsat the central station are otherwise in the condition illustrated inFigs. 1A, 1B, and 1C.

The first seven steps of the code transmitted by the central stationunder these conditions are identical with the first seven stepsdescribed above when the field station was transmitting the station callsignal only. Consequently, the description of these seven steps will notbe repeated, but the description will start with the beginning of theeighth code step.

The new positions of the levers 3I and 32 will, as hereinafter explainedin detail, cause the ninth and twelfth steps of the code to be madelong. The other steps will be short, except that the sixteenth step willbe long t reset all the apparatus at both the central station and thefield station to its original condition.

The original stick circuit for relay I23ST, which extended to terminal Bat back contact 0 of relay I23S, is replaced by another stick circuitwhen that relay picks up, which extends over front contact c of relay I238, terminals 99 and I00, wire I84 and back contact 0 of relay 8, toterminal B. As soon as relay SP picks up in response to energization ofrelay I23S, another connection to terminal B for the stick circuit forrelay I23ST is provided over front contact 0 of relay SP, wire I05, andback contact b of relay STP.

Eighth code step.-When relay R drops, its front contact a opens thecircuit for relay 2L and its front contact b opens the circuit forcounting chain relay I. At the same time, back contact c of relay Rcloses a circuit for relay IL and back contact d closes a circuit forrelay 8.

Front contact b of relay 8 closes a pickup circuit for chain repeatrelay CR, which circuit was previously traced in connection with thestation calling code. Relay CR completes its stick circuit, alsopreviously traced, over its front contact 1.

When relay CR picks up, its contacts a and b transfer control of thestick and hold-down circuits for transmitter relay T from the contacts aof the several counting chain relays and the stepping switch 20 to thefront contacts g of the several counting chain relays and the controllevers 3| and 32 for station I23, which are connected to the countingrelay contacts g through the terminals 31 and 36.

Front contact 1 of relay 8 completes a circuit for relay STP, which maybe traced from battery terminal B ,(Fig. 1E) over front contact a ofrelay I23ST, front contact b of relay I23S, terminals 34 and 35, wireI06, and front contact f of relay 8 to the winding of relay STP, andthence to the opposite battery terminal B.

When relay STP picks up, its front contact I) closes its stick circuitand its front contact 0 closes a stick circuit for electromagnet SM.

When relay 8 picks up, its back contact 0 opens one branch of the stickcircuit for relay I23ST and when relay STP picks up, its back contact bbreaks the last remaining branch of the stick circuit for relay I23ST.Relay I23ST therefore drops, and will not be picked up again until thestarting button 33 is again operated.

When relay 8 picks up, its front contact a opens the circuit of masterrelay M, and also prevents completion of the pickup circuit oftransmitter relay T when contact I of relay 1 closes. However, relay STPpicks up soon after relay 8, as above described, and its front contact ashunts the open back contact a of relay 8, thereby again completing thecircuit of master relay M and also completing the pickup circuit fortransmitter relay T. The release time of master; relay M is made longenough to bridge this short gap in the completion of its stick circuit.

When transmitter relay T picks up, it picks up relay R to terminate theeighth step of the code and start the impulse which constitute the ninthstep.

Relay T picks up before relay 2L releases, since its picking up is notdelayed by any of the holddown circuits. Hence the eighth code step is ashort one under the conditions described.

Ninth code step-When relay R picks up, its back contact 0 opens thecircuit to relay IL, and its back contact d opens the circuit tocounting chain relay 8. At the same time, front contact a of relay Rcloses the circuit for relay 2L and front contact b of relay R closes apickup circuit for counting chain relay I.

' I When relay I picks up, its back contact f opens the pickup circuitfor transmitter relay T, but its 76 backcontact g closes astick circuitfor relay T which includes front contact d of ma intricd. of relayCR,wire i, front-contact a of relay LP in parallel with front contact d ofrelay IL, front contact d of relay'T, and thence through the winding ofrelay T to the opposite battery terminal C. This stick circuit iseffective to keep the transmitter relay T energized until both relays ILand LP drop, and is thus effective to make the ninth code step long.

Relay iL, having been deenergized when relay R picked up, now releasesits contacts. Its front contact e opens the circuit of relay LP;

When back contact 1 of relay IL closes, it completes a circuit forindication registry relay 9; This circuit may be traced from batteryterminal B (Fig. 13) over front contact 0 of relay LBP, back contact ofrelayIL,' wir'e 59; front contact c of relay CR, front contacth of relayI, and thence through the winding'of'relay 9 to the opposite batteryterminal C. Relay 9 in picking up completes its own stick circuit at itsfront contact a. This stick circuit for relay 9 may be traced over frontcontact e of relay LBP, over wire 88 and the front contact a. of relay 9to its winding, and thence to the opposite battery terminal C. Theoperation'o'f relay 9 at this time is ineffective to produceany'controlor indication effect. It is mentioned here only to make thedescription of the operation complete.

Relay LP having been deenergized, now releases its contacts, and itsfront contact a is effective to open the stick circuit for transmitterrelay T, previously traced, which consequently drops, thereby droppingrelay R to terminate theninth code step. a I

Tenth code step.When relay R drops, its front contact a opens-thecircuit of relay 2L and its back contact 0 closes the circuit for relayIL, Front contact e of relay IL in turn closes the circuit for relay LP.At the same time, front contact I) of relay R opens the circuit of relayI- and back contact d of relay R completes a circuit for relay 2. Relay2, in picking up, immediately drops relay i and back contact 1 of relayIcompletes the pickup circuit for transmitter relay T, which picks up,thereby picking up relay R to terminate the tenth step and start theeleventh.

Since the hold-down circuit for relay T is not completed, relay T picksup promptly when relay l drops, thereby making the tenth code step ashort one.

Eleventh code step-When relay R picks up, its front contact a closes thecircuit for relay 2L and its back contact 0 opens the circuit for relayIL. At the same time,,back contact (1 of relay R opens the circuit ofrelay 2 and front contact b of relay R closes the circuit for relay 3.When relay 3 picks up, its back contact ,7 opens the circuit oftransmitter relay T, which releases its contacts, thereby dropping relayR. This terminates the-'eleventh'code step and starts the twelfth.

Twelfth code step-When relay R drops, its front contact a opens thecircuit ofrelay 2L and its back contact 0 completes the circuit'forrelay IL. At the same time, its front contact In opens the circuit ofrelay-3 and-its backcontactd closes the circuit of relay 4.

' Whenrelay 4 picks up; it completesover its front, contact g'ahold-down circuit for transmitter relay-T. This hold-down circuit may betraced from "battery terminal B (Fig. 1E) over control lever 32; frontcontact e of relay I238. terminals 3"I4 and 36-4- (Fig. 10), frontcontact g of relay 4-, front contact 12- of relay CR, wire 52, frontcontact 0 of relay LP in parallel with front contact 1 of relay 2L, backcontact e of relay T, and thence through resistances 5| and 52 to theopposite battery terminal (3. This hold-downcircuitremains completeduntil both relays 2L and LP release their contacts, and therebyinsuresthat thetwelfthcode step is long.

Relay 2L, having been deenergized'when relay R. dropped, releasesitscontacts, thereby opening. the circuit for relay LP; At the sametime, back-contact g of relay 2L completes an energizing circuit forindication registry relay I2. This circuit maybe traced over frontcontact 0 of'relay LBP, back contact g of relay 2L, wire 63,- frontcontact dof relay CR, front contact h of relay l, and thence through thewinding of relay I'Zto battery terminal-C. Relay I2 in picking upcompletes its own stick circuit over its front contact a similar to thestick circuit of registry relay 9. As in the case of relay 9, relay itperforms no indicating or control function during this phase of thesystem operation;

Relay-LP, having been deenergized when relay 2L released its contacts,now drops, opening the hold down circuit for transmitterrelay T, whichpicks up, in turn picking up relay -R to terminate the twelfth code stepandstart thethirteenth.

Thirteenth, fourteenth, and fifteenth code steps.Thethirteenth andfifteenth code steps are g'enerallysimilar to-the othershortodd-numbfer'cd steps, such astheeleventh. The fourteenth step is-similarto the other even-numbered short-steps, such as the tenth. It isbelieved that any further detailed description is unnecessary.

Sixteenthcode step-When relay R drops, it opens the circuit of relay 2Lat'its front contact to and closesthe circuit of relay IL at its backcontact c. At the same time, front contact I) of relay- R opens thecircuit of relay I and back contact d of relay R completes a pickupcircuit for counting chainrelay it. This circuit may be traced over backcontact d of relay R, front contact-d of relay LBP, wire 52, backcontact'e' of relay 6, front contact 01 of relay I, front contact e offirelay CR, backcontactg of relay 8, and thence through the winding ofrelay I6.

When relay I5-picks up, it closes its own stick circuit at it frontcontact e, and its front contact it opens the stick circuit of masterrelay M and the pickup circuit of transmitter relay T. Relay 2L, havingbeen deenergized at the beginning of the sixteenth step, now drops, andthe relays LP, LB; and LBP of the timing chain drop in their turn. Whenrelay-LBP drops, its front contact 0. opens the circuit of relay IL,whose contacts remain up because of its slow releasing characteristics.

When relay LBP drops, its front contact e opens thestick circuits forregistry relays 9 and I2, and its front contact 0 opens the stickcircuits for relays CR," I23S,-- and SP, so thateach oftheserelaysreleases. When relay SP drops, itsfrontcontact 0 opens the stick circuitfor relay STP, and as the latter relay drops its front 'contactcopensthe stick circuit for electromagne't SMof the stepping switchlfl; Aspreviously described, this causes =the-arm-2I toadvance onestep-so-thatthecentral stationwill call the next

